The p53 tumor suppressor gene is a sequence-specific transcription factor that activates the expression of genes engaged in promoting growth arrest or cell death in response to genotoxic stress. A role forp53- related modulation of neuronal viability has been suggested by the finding that p53 expression is elevated in damaged neurons in acute models of injury such as ischemia and epilepsy and in brain tissue samples derived from patients with chronic neurodegenerative diseases. Moreover, the absence of p53 has been shown to protect neurons from a wide variety of acute toxic insults consistent with the hypothesis from our previous applications that p53 expression regulates neuronal viability after injury. Our long-range objective is to assess the consequences of p53 gene expression in the CNS. However, the downstream molecular consequences of p53 activation in neurons remain obscure. Our proteomic analyses demonstrate that p53 is associated with injury-induced alterations in the expression of proteins that reside in or associate with the mitochondria. Mitochondrial dysfunction is a hallmark of stress-induced neuronal toxicity. Therefore, in the present application, we propose to test the hypothesis that p53 promotes neuronal cell death by altering the expression or distribution of proteins that regulate mitochondrial integrity. We will specifically: 1) Determine if the p53 protein promotes a loss of mitochondrial integrity and changes in cytoskeletal organization through the induction and mitochondrial translocation of cofilin; 2) Determine if the p53 protein promotes mitochondrial dysfunction and neuronal death by regulating the N-BAK protein; 3) Determine if dynamin- related protein-1 (Drp1) promotes mitochondrial dysfunction and neuronal death, and 4) Identify p53- dependent changes in the mitochondrial proteome. These studies will help elucidate the mechanism by which p53 regulates neuronal survival and activity in response to injury and neurologic disease.